1. Field of the Invention
The present invention relates generally to a reinforced multicore optical fiber coupler formed by fusing and extending a plurality of optical fibers.
2. Description of the Related Art
It has been recognized that, due to the small diameter of optical fiber couplers (e.g., preferably sized to have an outer diameter on the order of 10 .mu.m), an external force or temperature change can cause its propagation characteristics to change and, in some cases, cause physical damage to the coupler.
A now conventional way of dealing with this problem has been to use a reinforcing base having substantially the same coefficient of linear expansion as that of quartz. The reinforcing base protects the optical fibers from external forces so as to allow them to maintain a stable characteristic. One example of such a reinforcing base is the plate-like member disclosed in Japanese Utility Model Unexamined Publication No. Sho. 64-24308. Another example of such a reinforcing base is the pipe-like member disclosed in Japanese Patent Unexamined Publication No. Sho. 64-63907. A thermosetting or ultraviolet setting adhesive of an epoxy group, an urethaneacrylate group, or a cyanoacrylate group has been used as a fixing adhesive in such conventional optical fiber couplers.
Recently, advances in the technology of optical fiber communication lines have resulted in systems having a higher density of such lines, as well as an increase in the number of optical fiber couplers used. However, these advances have caused further problems to be overcome. Conventional couplers are constituted by a pair of optical fibers. By increasing the density of the optical fiber communication lines and the required number of optical fiber couplers, the lines and couplers take up a considerable amount of space. Moreover, complications arise in accommodating the residual length of the optical fibers on the opposite ends of the optical fiber coupler.
To overcome these problems, it is known to form an optical fiber coupler constituted by two optical fibers fixed on a reinforcing material. A plurality of reinforcing materials are accommodated in a single package. The optical fibers outside the package are formed into a tape-like multicore coated optical fiber bundle. An example of this conventional arrangement is disclosed in Japanese Patent Unexamined Publication No. Hei. 1-295211. Further known in the art is an arrangement in which optical fiber couplers, each containing two optical fibers, are arranged on a comb-tooth-like fixing member having a plurality of grooves that provide reinforcement. An example of such an arrangement is disclosed in Japanese Patent Unexamined Publication No. Sho. 63-254406.
In the conventional arrangements disclosed in Japanese Patent Unexamined Publication Nos. Hei 1-295211 and Sho. 63-254406, however, the optical fibers mounted on the optical fiber couplers are of a high density. Due to the high density of the optical fibers, a long time is required for forming a multicore optical fiber coupler according the foregoing arrangements.
To overcome the above mentioned problem of delay in forming the multicore optical fiber coupler, it is known in the art to directly produce a multicore optical fiber coupler from multicore coated optical fibers. An example of this method is disclosed in Japanese Patent Unexamined Publication No. Hei 1-120510. When coated optical fibers are fixed by using a reinforcing base, the whole non-extended portions and coating portions comprising the glass portions of the coated optical fibers are fixed by using an adhesive. This functions to thereby produce a multicore optical fiber coupler. Consequently, a problem arises in that deformation of the adhesive causes the transmission characteristic of the optical fiber coupler to undergo remarkable change when subjected to external forces, such as a temperature change and high humidity.